This proposal represents a biochemical-genetic study of the regulation of protein synthesis by bacteriophage T4. The focus is primarily biochemical and extrapolates from our earlier genetic and physiological findings. Major emphasis is on the T4 regA gene, which controls a post-transcriptional mechanism that represses the synthesis of many T4 early proteins. In Project 1 we will purify the protein product of the wild-type gene regA and several mutant forms of the protein having altered specificity in vivo; these proteins will be studied in an in vitro translation system in hopes of mimicking the in vivo effects and learning the mechanism of general repression and of autogenous regulation of the regA protein. In Project 2 we will measure the possible binding of regA protein to T4 mRNA, and seek other T4 proteins that bind to mRNA, using nitrocellulose-filter binding assays and affinity chromatography on immobilized mRNA. We will also try to identify the structural genes of these proteins. In Project 3 we will measure the possible binding of regA protein to ribosomes, and seek other T4 proteins that bind to ribosomes; we will seek to identify their genes as well as those of two, low-molecular-weight, T4 proteins we have already found on ribosomes. In Project 4 we will try to develop affinity-chromatography columns of immobolized ribosomes, to aid in identifying and purifying T4 proteins that bind specifically to ribosomes. In Project 5 we will attempt to describe comprehensively the patterns of coordinate expression of T4 strutural genes coding for proteins that bind to E. coli RNA polymerase; we have evidence for such coordinate expression.